It is well known in the art that liquid crystalline polyesters (LCP's) give anisotropic mechanical properties when injection molded or extruded. This behavior can be attributed to processing the LCP in its liquid crystalline or thermotropic state, resulting in the molded or extruded article being highly oriented with very high mechanical properties in the direction of flow and poorly oriented with low properties across the direction of flow. Such properties are said to be anisotropic.
The isotropic transition temperature of a polymer is the temperature at which the polymer melt changes from an opaque, thermotropic, anisotropic state to a clear, isotropic state. For some applications, it would be highly advantageous if polyester compositions were available which had isotropic transition temperatures low enough for them to be processed in their isotropic state. Such compositions should give much less anisotropic properties under certain processing conditions.
U.S. Pat. No. 4,067,852 broadly discloses certain melt processable, wholly aromatic polyesters, but no mention is made of low isotropic transition temperatures. Additionally, European Patent Application 0,356,226 discloses certain aromatic polyesters and polyester amides, but again, no mention is made of low isotropic transition temperatures.